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Getting a COVID-19 vaccine is an important tool — along with wearing a cloth mask, socially distancing and good hand hygiene — to help stop the ongoing pandemic. As wide-scale vaccination efforts continue, many people have questions about the vaccines. Mayo Clinic's Vaccination and Distribution Workgroup has answered some of the most common questions about COVID-19 vaccines.
What are the benefits of getting a COVID-19 vaccine?
A COVID-19 vaccine might:
- Prevent you from getting COVID-19 or from becoming seriously ill or dying due to COVID-19
- Prevent you from spreading the virus that causes COVID-19 to others
- Add to the number of people in the community who are protected from getting COVID-19 — making it harder for the disease to spread and contributing to herd immunity
- Prevent the virus that causes COVID-19 from spreading and replicating, which allows it to mutate and possibly become more resistant to vaccines
Should I get the COVID-19 vaccine even if I've already had COVID-19?
Getting COVID-19 might offer some natural protection or immunity from reinfection with the virus that causes COVID-19. It’s estimated that infection with the virus that causes COVID-19 and vaccination both result in a low risk of another infection with a similar variant for at least 6 months.
Because reinfection is possible and COVID-19 can cause severe medical complications, it’s recommended that people who have already had COVID-19 get a COVID-19 vaccine.
In addition, COVID-19 vaccination might offer better protection than getting sick with COVID-19. A recent study showed that unvaccinated people who already had COVID-19 are more than twice as likely as fully vaccinated people to be reinfected with COVID-19.
Recent research also suggests that people who got COVID-19 in 2020 and then received mRNA vaccines produce very high levels of antibodies that are likely effective against current and, possibly, future variants. Some scientists call this hybrid immunity. Further research is needed.
What COVID-19 vaccines have been authorized or approved and how do they work?
Currently, several COVID-19 vaccines are in clinical trials. The FDA continues to review the results of these trials before approving or authorizing COVID-19 vaccines for use. But because there is an urgent need for COVID-19 vaccines and the FDA's vaccine approval process can take months to years, the FDA first gave emergency use authorization to COVID-19 vaccines based on less data than is normally required. The data must show that the vaccines are safe and effective before the FDA can give emergency use authorization or approval.
Vaccines with FDA emergency use authorization or approval include:
- Pfizer-BioNTech COVID-19 vaccine
The FDA has approved the Pfizer-BioNTech COVID-19 vaccine, now called Comirnaty, to prevent COVID-19 in people age 16 and older. The FDA approved Comirnaty after data found the vaccine is safe and effective. The Pfizer-BioNTech COVID-19 vaccine is 91% effective in preventing the COVID-19 virus with symptoms in people age 16 and older. The vaccine is still under an emergency use authorization for children ages 12–15. The vaccine is 100% effective in preventing COVID-19 in children ages 12–15. It requires two injections given 21 days apart. The second dose can be given up to six weeks after the first dose, if needed. The vaccine also now is available under an emergency use authorization for children ages 5–11. This vaccine is about 91% effective in preventing COVID-19 in children ages 5–11. It requires two injection, given 21 days apart. It also contains a lower dose than the Pfizer-BioNTech COVID-19 vaccine used for people age 12 and older.
- Moderna COVID-19 vaccine
The Moderna COVID-19 vaccine is 94% effective in preventing COVID-19 with symptoms. This vaccine is authorized for people age 18 and older. It requires two injections given 28 days apart. The second dose can be given up to six weeks after the first dose, if needed.
- Janssen/Johnson & Johnson COVID-19 vaccine
In clinical trials, this vaccine was 66% effective in preventing the COVID-19 virus with symptoms — as of 14 days after vaccination. The vaccine also was 85% effective at preventing severe disease with COVID-19 — at least 28 days after vaccination. This vaccine is authorized for people age 18 and older. It requires one injection. The FDA and the Centers for Disease Control and Prevention (CDC) have recommended that use of this vaccine continue in the U.S. because the benefits outweigh the risks. If you are given this vaccine, you should be educated about the possible risks and symptoms of a blood clotting problem.
Both the Pfizer-BioNTech and the Moderna COVID-19 vaccines use messenger RNA (mRNA).
Coronaviruses have a spike-like structure on their surface called an S protein. COVID-19 mRNA vaccines give cells instructions to immune cells for how to make a harmless piece of an S protein. After vaccination, your cells begin making the protein pieces and displaying them on cell surfaces. Your immune system will recognize the protein and begin building an immune response and making antibodies. The mRNA in the vaccine doesn't enter the nucleus of the cell, where DNA is kept.
The Janssen/Johnson & Johnson COVID-19 vaccine is a vector vaccine. In this type of vaccine, material from the COVID-19 virus is inserted into a different kind of weakened live virus, such as an adenovirus. When the weakened virus (viral vector) gets into your cells, it delivers material from the COVID-19 virus that gives your cells instructions to make copies of the S protein. Once your cells display the S proteins on their surfaces, your immune system responds by creating antibodies and defensive white blood cells. If you become infected with the virus that causes COVID-19, the antibodies will fight the virus.
Viral vector vaccines can't cause you to become infected with the COVID-19 virus or the viral vector virus. Also, the genetic material that's delivered doesn't become part of your DNA.
If I am vaccinated and develop side effects, should I get tested?
While many people do not have reactions after vaccination, it is normal if you do. It does not mean you have the COVID-19 infection. If you have a reaction, take some time to rest and allow your body to recover.
These reactions should not keep you from going to work or doing other activities. However, stay home if you have a fever. It is not necessary to have a COVID-19 test or to quarantine.
What are the possible side effects of the COVID-19 vaccine?
A COVID-19 vaccine can cause mild side effects after the first or second dose, including:
- Pain, redness or swelling where the shot was given
- Muscle pain
- Joint pain
- Nausea and vomiting
- Feeling unwell
- Swollen lymph nodes
You’ll be monitored for 15 minutes after getting a COVID-19 vaccine to see if you have an allergic reaction. Most side effects go away in a few days. Side effects after the second dose might be more intense. Many people have no side effects.
A COVID-19 vaccine may cause side effects similar to signs and symptoms of COVID-19. If you’ve been exposed to COVID-19 and you develop symptoms more than three days after getting vaccinated or the symptoms last more than two days, self-isolate and get tested.
Can I get a COVID-19 vaccine if I have an existing health condition?
Yes, if you have an existing health condition you can get a COVID-19 vaccine — as long as you haven’t had an allergic reaction to a first dose of a COVID-19 vaccine or any of its ingredients. But there is limited information about the safety of the COVID-19 vaccines in people who have weakened immune systems or autoimmune conditions.
COVID-19 vaccines also might not fully protect people from COVID-19 who have a weakened immune system that is caused by HIV, certain conditions or medications. It might be necessary to continue taking precautions.
What are the long-term side effects of the COVID-19 vaccines?
Because COVID-19 vaccines clinical trials only started in the summer of 2020, it’s not yet clear if these vaccines will have long-term side effects. However, vaccines rarely cause long-term side effects.
If you’re concerned, in the U.S., safety data on COVID-19 vaccines will be reported to a national program called the Vaccine Adverse Event Reporting System. This data is available to the public. The CDC has also created v-safe, a smartphone-based tool that allows users to report COVID-19 vaccine side effects. If you have additional questions or concerns about your symptoms, talk to your doctor.
Is it safe to use fever-reducing pain medications like acetaminophen before or after receiving the COVID-19 vaccine?
It isn’t recommended that you take an over-the-counter medication before getting a COVID-19 vaccine to prevent possible discomfort. It’s not clear how these medications might impact the effectiveness of the vaccines. However, it’s OK to take this kind of medication after getting a COVID-19 vaccine, as long as you have no other medical reason that would prevent you from taking it.
Do the COVID-19 vaccines protect against the COVID-19 variants?
In the U.S., the delta (B.1.617.2) variant is now the most common COVID-19 variant. It is nearly twice as contagious as earlier variants and might cause more severe illness.
While research suggests that COVID-19 vaccines are slightly less effective against the variants, the vaccines still appear to provide protection against severe COVID-19.
- Early research from the U.K. suggests that, after full vaccination, the Pfizer-BioNTech COVID-19 vaccine is 88% effective at preventing symptomatic COVID-19. The vaccine is also 96% effective at preventing severe disease with COVID-19 caused by the delta variant.
- Early research from Canada suggests that, after one dose, the Moderna COVID-19 vaccine is 72% effective at preventing symptomatic COVID-19 caused by the delta variant. One dose of the vaccine is also 96% effective at preventing severe disease with COVID-19 caused by the delta variant.
- The Janssen/Johnson & Johnson COVID-19 vaccine is 85% effective at preventing severe disease with COVID-19 caused by the delta variant, according to data released by Johnson & Johnson.
What COVID-19 vaccines have vaccine has been approved for kids?
In the U.S., COVID-19 vaccines are available to children by age group:
- Ages 5–11
The U.S. Food and Drug Administration (FDA) has given emergency use authorization to a Pfizer-BioNTech COVID-19 vaccine for this age group. This vaccine involves two injections, given three weeks apart. It contains a lower dose than the Pfizer-BioNTech COVID-19 vaccine used for people age 12 and older. Research shows that this vaccine is about 91% effective in preventing COVID-19 in children ages 5–11.
- Ages 12–15
The FDA has given emergency use authorization to a Pfizer-BioNTech COVID-19 vaccine for this age group. This vaccine involves two injections, given three weeks apart. It contains the same dose as the Pfizer-BioNTech COVID-19 vaccine for people ages 16 and older. The second dose can be given up to six weeks after the first dose, if needed.
Research has shown that this vaccine is 100% effective in preventing COVID-19 in children ages 12–15.
- Ages 16 and older
The FDA has approved a Pfizer-BioNTech COVID-19 vaccine, now called Comirnaty, for this age group. This vaccine involves two injections, given three weeks apart. The second dose can be given up to six weeks after the first dose, if needed. This vaccine is 91% effective in preventing severe illness with COVID-19 in people age 16 and older.
Is there any difference in the ingredients or dosing of the Pfizer-BioNTech COVID-19 vaccines for younger children, older children or adults?
The Pfizer-BioNTech COVID-19 vaccine for children ages 5–11 contains a lower dose (10 micrograms) than the vaccine used for older children and adults (30 micrograms). (58) Smaller needles are being used to deliver the vaccine to children ages 5–11.
The Pfizer-BioNTech COVID-19 vaccine for children ages 5–11 also contains a different buffer than the vaccine used for older children and adults. This different buffer, which is used in other FDA-approved vaccines, will help keep the vaccine stable in refrigerated temperatures for longer.
The ingredients and dosing of the Pfizer-BioNTech COVID-19 vaccine are the same for children ages 12–15 and people age 16 and older.
If children don’t frequently experience severe illness with COVID-19, why do they need a COVID-19 vaccine?
A COVID-19 vaccine can prevent your child from getting and spreading the virus that causes COVID-19. If your child gets COVID-19, a COVID-19 vaccine could prevent him or her from becoming severely ill or experiencing short-term or long-term complications. Children with other health conditions, such as obesity, diabetes and asthma, might be at higher risk of serious illness with COVID-19.
Getting a COVID-19 vaccine can also help keep your child in school and more safely have playdates and participate in sports and other group activities.
How did the FDA determine the safety and effectiveness of the Pfizer-BioNTech COVID-19 vaccines for use in kids?
For kids ages 5–11, the FDA reviewed a vaccine study of more than 4,600 children in this age range. Of this group, about 3,100 were given the Pfizer-BioNTech COVID-19 vaccine. The other children were given an inactive (placebo) shot. Children who were given the vaccine were monitored for side effects for at least two months after the second dose. Side effects were generally mild to moderate.
The FDA also took an early look at cases of COVID-19 that occurred one week after children were given a second dose of the vaccine. None of the children in this analysis had been previously diagnosed with COVID-19. Among 1,305 children given the vaccine, there were three cases of COVID-19. Among 663 children given the placebo, there were 16 cases of COVID-19. The results suggest that the vaccine is about 91% effective in preventing COVID-19 in this age group.
For kids ages 12–15, the FDA reviewed a vaccine study of more than 2,200 U.S. children in this age range. Of this group, about half were given the Pfizer-BioNTech COVID-19 vaccine. The other children were given a placebo shot.
A week after the second dose was given, there were no cases of COVID-19 in the 1,005 children given the Pfizer-BioNTech vaccine. Among 978 children given the placebo, there were 16 cases of COVID-19. None of the children had previously been diagnosed with COVID-19. The results suggest that the vaccine is 100% effective at preventing the COVID-19 virus in this age group.
Also, a portion of the children in each age group were monitored for at least two months after being given the second dose.
Can someone who is vaccinated still transmit the COVID-19 virus?
It's not yet known whether a person who is vaccinated for COVID-19 can get an asymptomatic COVID-19 infection and spread that infection to another person. Those vaccinated for COVID-19 must practice the same safety precautions as those who are not vaccinated for COVID-19, including wearing a mask, practicing social distancing and washing their hands frequently.
What is known is that COVID-19 vaccines are 95% effective in preventing symptomatic COVID-19 infection.
Can pregnant or breastfeeding women get the COVID-19 vaccine?
If you are pregnant or breastfeeding, it's recommended that you get a COVID-19 vaccine. Getting a COVID-19 vaccine can protect you from severe illness due to COVID-19. Vaccination can also help pregnant women build antibodies that might protect their babies.
COVID-19 vaccines don't cause infection with the virus that causes COVID-19, including in pregnant women or their babies. None of the COVID-19 vaccines contain the live virus that causes COVID-19.
While further research is needed, early findings suggests that getting an mRNA COVID-19 vaccine during pregnancy poses no serious risks for pregnant women who were vaccinated or their babies. The findings are based on data from the CDC's coronavirus vaccine safety monitoring system. Also, keep in mind that mRNA COVID-19 vaccines don't alter your DNA.
In addition, vaccines that use the same viral vector as the Janssen/Johnson & Johnson COVID-19 vaccine have been given to pregnant women in each trimester of pregnancy in clinical trials. No harmful effects were found.
If you have concerns, talk to your health care provider about the risks and benefits of getting a COVID-19 vaccine.
Can a COVID-19 vaccine affect fertility or menstruation?
It's recommended that you get a COVID-19 vaccine if you are trying to get pregnant or might become pregnant in the future. There is no evidence that any COVID-19 vaccines cause fertility problems.
A small number of women have reported experiencing temporary menstrual changes after getting a COVID-19 vaccine. A small study has also shown that some women experienced temporary menstrual changes after getting COVID-19. It’s not clear if getting COVID-19 or a COVID-19 vaccine causes these changes. Further research is needed.
Keep in mind that many things can affect menstrual cycles, including infections, stress, sleep problems and changes in diet or exercise.
If you become pregnant after getting the first dose of a COVID-19 vaccine that requires two doses, it's recommended that you get your second shot.
Can COVID-19 vaccines affect the heart?
In the U.S., there has been an increase in reported cases of myocarditis and pericarditis after mRNA COVID-19 vaccination, particularly in males ages 12–17. Myocarditis is the inflammation of the heart muscle, while pericarditis is the inflammation of the lining outside the heart. These reports are rare. One study suggests that the risk of myocarditis in the week after being fully vaccinated with the Pfizer-BioNTech vaccine is about 54 cases per million doses given to males ages 12–17.
Of the cases reported, the problem happened more often after the second dose of the COVID-19 vaccine and typically within several days after COVID-19 vaccination. Most of the people who received care felt better after receiving medicine and resting.
Symptoms to watch for include:
- Chest pain
- Shortness of breath
- Feelings of having a fluttering or pounding heart
If you or your child has any of these symptoms within a week of getting a COVID-19 vaccine, seek medical care.
What are the symptoms of a blood clotting reaction to the Janssen/Johnson & Johnson COVID-19 vaccine?
Use of the Janssen/Johnson & Johnson COVID-19 vaccine might increase the risk of a rare and serious blood clotting disorder. Nearly all of those affected have been women ages 18 to 49, with the disorder happening at a rate of 7 for every 1 million vaccinated women in this age group. For women age 50 and older and men of all ages, the disorder is even more rare.
The FDA and the CDC have recommended that use of the vaccine in the U.S. can continue because the benefits outweigh the risks. Evidence of these blood clots haven’t been reported in the Pfizer-BioNTech or Moderna COVID-19 vaccines.
Serious side effects of the Janssen/Johnson & Johnson COVID-19 vaccine can occur within three weeks of vaccination and require emergency care.
Possible symptoms include:
- Shortness of breath
- Persistent stomach pain
- Severe or persistent headaches or blurred vision
- Chest pain
- Leg swelling
- Easy bruising or tiny red spots on the skin beyond the injection site
Mild to moderate headaches and muscle aches are common in the first three days after vaccination and don’t require emergency care.
Should people who have recovered from COVID-19 get vaccinated?
People who've had COVID-19 infection should still get vaccinated because the vaccine might provide them a longer duration of protection than COVID-19 itself would. This is something that we're still learning and, hopefully, we'll know more about over the next few months.
In general, we recommend that people should wait for about 90 days from infection before they get vaccinated. There is no harm if they get vaccinated beforehand. We know that they're fully protected from their own infection for the first three months, so they can wait for a few months before they get the vaccine and let the others get vaccinated.
Can I stop taking safety precautions after getting a COVID-19 vaccine?
You are considered fully vaccinated two weeks after you get a second dose of an mRNA COVID-19 vaccine or two weeks after you get a single dose of the Janssen/Johnson & Johnson COVID-19 vaccine. Currently, there is no time limit after vaccination on your fully vaccinated status
After you are fully vaccinated, you can more safely return to doing activities that you might not have been able to do because of the pandemic. You can also stop wearing a mask or social distancing in any setting, except where required by a rule or law. However, if you are in an area with a high number of new COVID-19 cases in the last week, the CDC recommends wearing a mask indoors in public and outdoors in crowded areas or when you are in close contact with unvaccinated people. If you are fully vaccinated and have a condition or are taking medications that weaken your immune system, you may need to keep wearing a mask.
You also will still be required to wear a mask on planes, buses, trains and other public transportation traveling to, within, or out of the U.S., as well as in places such as airports and train stations.
If you are traveling in the U.S., you don’t need to get tested before or after your trip or quarantine after you return. If you are traveling outside of the U.S., you don’t need to get tested before you leave the U.S. unless your destination requires it. You still need to show a negative test result or proof that you’ve recovered from COVID-19 in the past 3 months before boarding an international flight to the U.S. It’s also recommended that you get tested 3 to 5 days after international travel. However, quarantining isn’t needed.
If you’ve been fully vaccinated and you’ve had close contact with someone who has the COVID-19 virus, get tested 5 to 7 days afterward. And if you are a resident or employee of a correctional or detention facility or a homeless shelter and are around someone who has COVID-19, you should still get tested even if you don’t have symptoms of COVID-19.
Are COVID-19 vaccine additional doses or boosters recommended?
An additional dose of a COVID-19 vaccine is recommended for people who are fully vaccinated and might not have had a strong enough immune response. In contrast, a booster dose is recommended for some people who are fully vaccinated and whose immune response weakened over time.
The CDC recommends additional doses and booster doses of COVID-19 vaccines in specific instances:
- Additional dose
The CDC recommends a third dose of an mRNA COVID-19 vaccine for some people with weakened immune systems, such as those who have had an organ transplant. People with weakened immune systems might not develop enough immunity after vaccination with two doses of an mRNA COVID-19 vaccine. An additional dose might improve their protection against COVID-19. The third dose should be given at least 28 days after a second dose of an mRNA COVID-19 vaccine. The additional dose should be the same brand as the other two mRNA COVID-19 vaccine doses you were given. If the brand given isn’t known, either brand of mRNA COVID-19 vaccine can be given as a third dose.
- Booster dose
If you have been given both doses of the Pfizer-BioNTech COVID-19 vaccine or the Moderna COVID-19 vaccine and it’s been at least 6 months, you might be able to get a booster dose. The CDC recommends a booster dose for people age 65 and older and for people age 18 and older who live in long-term care settings, have an underlying medical condition, or live or work in a high-risk setting. If you have been given one dose of the Janssen/Johnson & Johnson COVID-19 vaccine and it’s been at least two months, you also might be able to get a booster dose. The CDC recommends a booster dose for people age 18 and older. You may choose which vaccine you get as a booster dose. You can get a booster dose that is the same brand as your previous shot or shots or choose a different brand.
Can someone who is vaccinated still transmit the COVID-19 virus?
It's not yet known whether a person who is vaccinated for COVID-19 can get an asymptomatic COVID-19 infection and spread that infection to another person. Those vaccinated for COVID-19 must practice the same safety precautions as those who are not vaccinated for COVID-19, including wearing a mask, practicing social distancing and washing hands frequently. What is known is that COVID-19 vaccines are 95% effective in preventing symptomatic COVID-19 infection.
Were COVID-19 vaccines manufactured using fetal tissue?
Neither the Pfizer/BioNTech COVID-19 vaccine nor the Moderna COVID-19 vaccine contain fetal cells, nor were fetal cells used in the production of either vaccine.
While the Janssen/Johnson & Johnson COVID-19 vaccine may have its production based on an adenovirus and historical immortalized embryonic cell origin, the vaccine does not contain embryonic cells. In addition, the Vatican has stated to get a vaccine dose irrespective of vaccine origin.
Can I still get COVID-19 after I'm vaccinated?
COVID-19 vaccination will protect most people from getting sick with COVID-19.
A very small percentage of fully vaccinated people will still get COVID-19 if they are exposed to the virus that causes COVID-19. These are called vaccine breakthrough cases. Some people might not experience any symptoms and some people could become sick due to COVID-19.
However, vaccination might make illness less severe. If you are fully vaccinated, the overall risk of hospitalization and death due to COVID-19 is much lower than among unvaccinated people with similar risk factors.
Should I delay getting COVID-19 vaccine if I've received another type of vaccine recently?
Mayo Clinic experts suggest that you consider delaying your vaccination for COVID-19 if you've received another vaccine within the past 14 days. You also should wait a couple of weeks after being vaccinated for COVID-19 to receive a different vaccine, like the flu vaccine.
While there is no reason to believe that one vaccine will interfere with another, when COVID-19 vaccines were being studied, research volunteers did not receive vaccines at the same time or within two to four weeks of being vaccinated for COVID-19. If you have a reaction after being vaccinated, separating vaccinations helps to correctly identify which vaccine may have been responsible.
Mayo Clinic experts have no concerns with the safety or effectiveness of COVID-19 vaccines for those who choose to be vaccinated for COVID-19 despite a recent vaccination.
Should I delay my COVID-19 vaccine if I am scheduled for surgery?
There is no need to postpone being vaccinated for COVID-19 until after your surgery. Any side effects, such as fever, that may occur from being vaccinated for COVID-19 the vaccine would will resolve within seven days. Most side effects resolve within three days.
Mayo does not recommend that you schedule your vaccination for COVID-19 within a few days of your surgery, especially the second dose of the Pfizer/BioNTech or Moderna vaccines for COVID-19. About 15% of people will experience a fever after the second dose of these vaccines. For the first dose, less than 1% will experience a fever.
If you check in on the day of surgery and you have a fever, you may need to reschedule your surgery. A fever immediately after surgery raises concerns about a surgical wound infection, so it's ideal if you can allow a week between being vaccinated for COVD-19 and surgery, especially for the second dose.
- Get information about Mayo Clinic's COVID-19 vaccination plan.
- Get vaccination updates by Mayo Clinic Health System regions.
- Find out what pregnant or breastfeeding women should know about COVID-19 vaccines.
Information in this post was accurate at the time of its posting. Due to the fluid nature of the COVID-19 pandemic, scientific understanding, along with guidelines and recommendations, may have changed since the original publication date.